Core and pattern manufacture for investment casting

ABSTRACT

Method and apparatus for making a ceramic core or fugitive pattern for use in investment casting wherein a fluid ceramic core or pattern material is introduced into a molding cavity defined by cooperating dies, and at least a region of one or both of the dies is heated during filling of the molding cavity with the material and then cooled to a lower ejection temperature before removal of a ceramic core or pattern from the molding cavity.

FIELD OF THE INVENTION

[0001] The present invention relates to manufacture of ceramic cores andfugitive patterns for use in making shell molds for investment castingof metals and alloys.

BACKGROUND OF THE INVENTION

[0002] In casting hollow gas turbine engine blades and vanes (airfoils)using conventional equiaxed and directional solidification techniques, afired ceramic core is positioned in a ceramic investment shell mold toform internal cooling passageways in the airfoil. During service in thegas turbine engine, cooling air is directed through the passageways tomaintain airfoil temperature within an acceptable range. The firedceramic core used in investment casting of hollow turbine engineairfoils typically has an airfoil-shaped region with a thincross-section trailing edge region.

[0003] The ceramic core typically is formed to desired coreconfiguration by injection molding, transfer molding or pouring of anappropriate fluid ceramic core material that includes one or moreceramic powders, a binder, and optional additives into a suitably shapedcore molding die. After the green molded core is removed from the die,it is subjected to firing at elevated (superambient) temperature in oneor more steps to remove the fugitive binder and sinter and strengthenthe core for use in casting metallic material, such as a nickel orcobalt base superalloy typically used to cast hollow gas turbine engineblades and vanes (airfoils).

[0004] The fired ceramic core then is used in manufacture of the shellmold by the well known lost wax process wherein the ceramic core isplaced in a pattern molding die and a fugitive pattern is formed aboutthe core by injecting under pressure pattern material, such as wax,thermoplastic and the like, into the die in the space between the corethe inner die walls. The pattern typically has an airfoil-shaped regionwith a thin cross-section trailing edge region corresponding in locationto trailing edge features of the core.

[0005] The fugitive pattern with the ceramic core therein is subjectedto repeated steps to build up the shell mold thereon. For example, thepattern/core assembly is repeatedly dipped in ceramic slurry, drained ofexcess slurry, stuccoed with coarse ceramic stucco or sand, and then airdried to build up multiple ceramic layers that form the shell mold onthe assembly. The resulting invested pattern/core assembly then issubjected to a pattern removal operation, such as steam autoclaving, toselectively remove the fugitive pattern, leaving the shell mold with theceramic core located therein. The shell mold then is fired at elevatedtemperature to develop adequate shell mold strength for metal casting.

[0006] Certain complex features at the thin cross-section trailing edgeregion of the ceramic core and fugitive pattern used in investmentcasting of turbine airfoils (e.g. turbine blades) have presentedmanufacturing difficulties. In particular, the thin cross-sectiontrailing edge region of the core includes multiple narrow spaced apartribs that will form narrow cooling air exit openings at the trailingedge of the cast turbine blade.

[0007] The core molding die is machined to include spaced apart wallfeatures that define therebetween narrow channels that will form theceramic core ribs when filled with ceramic core material. These narrowchannels have been difficult to completely fill during the coreinjection molding operations. In most cases, the ceramic core materialentering the channels solidifies prematurely prior to completely fillingthe channels and forces remaining ceramic material to flow around theblockages through core print regions of the molding cavity and enter thechannels from the opposite side where unfortunately another prematurelysolidified front is formed in the channels. During the so-called highpressure packing phase of the core molding cycle following a fill cycle,the prematurely solidified fronts located in the channels are pushed and“forged” together, resulting in formation of a so-called weld or knitline where the prematurely solidified fronts are “forged” together underthe packing pressure. These weld or knit lines are relativelymechanically weak areas that can easily break or fracture during normalcore processing and handling, resulting in scrapping of the core. Theseproblems have persisted even after high die fill speeds (e.g. less than150 milliseconds fill time), high ceramic material temperatures, andhigh packing pressures (e.g. 2000 psi) have been employed in pastattempts to overcome the problem of inadequate filling of the channelsat the trailing edge regions of the core molding die maintained at 80degrees F. plus or minus 5 degrees F. by control of press platentemperature. Moreover, such injection parameters provide an unstablepressure profile during the molding operation.

[0008] Similar problems have been experienced in filling of thincross-section trailing edge regions and other regions of the fugitivepattern injection molding die.

[0009] An object of the present invention is to provide improved methodand apparatus for making ceramic cores and fugitive patterns for use ininvestment casting of metals and alloys.

SUMMARY OF THE INVENTION

[0010] In an embodiment of the invention, a fluid material having acomposition selected to form a ceramic core or a fugitive pattern isintroduced into a molding cavity defined by cooperating dies. At least aregion of one or both dies proximate a hard-to-fill region of themolding cavity is heated to a superambient temperature prior to andduring filling of the molding cavity with the fluid material followed bycooling thereof to a lower ejection temperature before removal of amolded ceramic core or a molded pattern from the molding cavity.

[0011] In an embodiment of the invention to make a molded airfoil-shapedbody of ceramic core material or pattern material, the heated/cooled dieregion is located proximate a hard-to-fill, thin cross-section trailingedge region or other region of an airfoil-shaped molding cavityconfigured to form the body.

[0012] In another embodiment of the invention, at least a region of oneor both of the dies is heated/cooled by one or more thermoelectricelements disposed on one or both of the dies. A temperature sensor isdisposed proximate the region, and an electrical power controller isconnected to the thermoelectric element (s) to control electrical powerthereto in response to sensed temperature.

[0013] The invention provides apparatus for molding an airfoil-shapedbody for use in casting of a metallic airfoil. The apparatus comprisesfirst and second dies defining a molding cavity having an airfoil-shape,and at least one thermoelectric element disposed on at least one of thedies proximate a hard-to-fill region of the molding cavity to heat thatregion during filling of the molding cavity with fluid material and tocool the region to a lower ejection temperature before a moldedairfoil-shaped body is removed from the molding cavity. The apparatuscan include an inlet conduit for conducting a heat exchange fluid toremove heat from each thermoelectric element and an outlet conduit forexhausting the heat exchange fluid therefrom. The molding cavity has aconfiguration of a ceramic core or a fugitive pattern that replicatesthe airfoil-shaped body.

[0014] The above objects and advantages of the present invention willbecome more readily apparent from the following detailed descriptiontaken with the following drawings.

DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic view of a die assembly of an injectionmolding press.

[0016]FIG. 2 is a sectional view of upper and lower molding dies of FIG.1.

[0017]FIG. 3 is a top elevation view of the lower molding die havingthermoelectric elements thereon pursuant to an embodiment of theinvention.

[0018]FIG. 3A is a top elevation view similar to FIG. 3 of a lowermolding die having thermoelectric elements thereon pursuant to anotherembodiment of the invention.

[0019]FIG. 3B is a top elevation view similar to FIG. 3 of a lowermolding die having fluid passages pursuant to another embodiment of theinvention.

[0020]FIG. 4 is a perspective view of a ceramic core manufactured inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to manufacture of molded ceramiccores and fugitive patterns for use in making shell molds for investmentcasting of metals and alloys. The invention is especially useful inmaking ceramic cores and fugitive patterns for use in the casting ofnickel based and cobalt based superalloys to form hollow gas turbineengine airfoils such as turbine blades and vanes using conventionalequiaxed to produce equiaxed grain airfoils and directionalsolidification techniques to produce columnar grain and single crystalairfoils. However, the invention is not so limited and can be practicedto make ceramic core and fugitive patterns for use in casting of othermetallic components.

[0022] The invention is useful to provide filling of one or morehard-to-fill regions of the molding cavity where fluid ceramic corematerial or fugitive pattern material has difficulty in filling theregion(s). A hard-to-fill region of the molding cavity can be difficultto fill with fluid material by virtue of its thin cross-sectionaldimension or other dimension(s), complex configuration, remoteness fromthe inlet of the fluid material into the molding cavity, local rapidheat loss through dies, flow characteristics of the fluid materialproximate the region, and combinations of these factors. The inventioncan be practiced to fill such a hard-to-fill region(s) of the moldingcavity with fluid ceramic core material or fluid pattern material in themolding of ceramic cores and fugitive patterns for use in investmentcasting. Although the invention is described below for purposes ofillustration with respect to filling of a thin cross-section trailingedge region of an airfoil-shaped core molding cavity, the invention isnot so limited and can be practiced to fill any hard-to-fill region ofthe mold cavity, regardless of location in the molding cavity. Forexample, the invention can be practiced to improve filling of one ormore hard-to-fill region(s) at the leading edge of the ceramic core orfugitive pattern.

[0023] For purposes of illustration and not limitation, FIG. 1illustrates first and second cooperating dies 10, 12, which aremaintained at 82-83 degrees F. by water cooled aluminum plates 23 a, 23b disposed between fixed press platen 25 a and die base 27 a and movablepress platen 25 b and die base 27 b of the injection molding press. Thedie base 27 a holds die 10 while the die base 27 b holds die 12. Thewater cooled plates 23 a, 23 b each includes a cooling water inlet I tosupply cooling water to a water passage (not shown) in each plate 23 a,23 b and then out a water outlet L. In lieu of, or in addition, tocooling plates 23 a, 23 b, the die bases 27 a, 27 b can be similarlywater cooled to maintain overall die temperature except at local dieregion 30.

[0024] FIGS. 1-3 illustrate cooperating core molding dies 10, 12 asdefining a main core molding cavity 14 therebetween having a generalairfoil shape. The dies 10, 12 typically are made of steel althoughother suitable die materials can be used. The molding cavity 14typically includes complex die surface features such as turbulators,channels, pedestal recesses and the like, as dictated by a particularcore design, to be molded onto the core but which are omitted in FIG. 3as they form no part of the invention. The airfoil-shaped mold cavity 14includes a leading edge region 14 a and a trailing edge region 14 b thattapers to a relatively thin cross-section as compared to thecross-section of the main core cavity 14. For example only, the trailingedge region 14 b can taper down to a thickness of less than 0.014 inch.This compares to a maximum thickness of 0.500 inch of core moldingcavity 14 near the leading edge region. The leading region and trailingedge regions 14 a, 14 b of the molding cavity 14 form respective leadingand trailing edges LE, TE on the molded core C.

[0025] Wall features 14 c are machined on the lower die 10 and upper die12 to cooperate when the dies are closed to define narrow channels 14 dtherebetween. The narrow channels 14 d form narrow ceramic ribs Rseparated by open spaces OP on the ceramic core C, FIG. 4, that ismolded in the molding cavity 14. The ribs R will form exit openings forcooling air from the trailing edge of the cast superalloy turbineairfoil when the core is removed therefrom in a manner known in theairfoil casting art.

[0026] The die 10 includes a molding surface 14 e to form a convexairfoil-shaped core surface S1, and the die 12 includes a moldingsurface 14 f to form a concave airfoil-shaped core surface S2 on themolded core C, FIG. 4. The molding cavity 14 includes secondary regions14 g, 14 h that are adapted to form core print regions P1, P2 on themolded core C. A plurality (3 shown) of air vent passages 14 p aredisposed between the trailing edge region 14 d and grooves 14 g to ventair from molding cavity 14 as ceramic core material is introduced intothe cavity 14.

[0027] A plurality of ejector pins EP are disposed in the die 10 andmovable in a manner to eject the molded core C from the molding cavity14. Ejector pins EP proximate the trailing edge region 14 b are shown inFIG. 3. Other ejector pins located at various other locations in themolding cavity 14 to effect removal of the molded core therefrom inconventional manner are not shown.

[0028] An inlet opening 10 a is formed in the lower die 10 or upper die12, or both, and communicated to a pump P of a conventional coreinjection molding press (not shown). Ceramic core material, such as afluid ceramic compound, is injected under pressure (e.g. only 500 to2000 psi) into the molding cavity 14 via opening 10 a. The dies 10, 12and pump P can be part of a conventional hydraulic ceramic coreinjection molding press available as model DCS-2 from Howmet TempcraftInc., Cleveland, Ohio. The injection molding press is operated toprovide a fill stage during which ceramic core material is injectedunder pressure at constant injection ram speed or volumetric rate intothe molding cavity 14, a pack stage during which the ceramic corematerial pressure is increased and stabilized to fully fill the moldcavity 14, a hold stage during which pressure on the ceramic corematerial is maintained until core solidification is complete, and a coreejection stage when the dies are opened to allow removal of the moldedcore. Solidification occurs as a result of heat loss from the ceramiccore material into the dies 10, 12.

[0029] The fluid ceramic core compound injected into the molding cavity14 comprises a mixture of one or more suitable ceramic powders (flours),a fugitive binder and other constituents such as one or more fugitivefiller materials, dispersants, plasticizers, lubricants and otherconstituents. The binder can be a thermoplastic wax-based binder, athermoplastic resin, or an organometallic liquid, such as prehydrolizedethyl silicate, mixed with the ceramic powder(s) in appropriateproportions to form a ceramic powder/binder mixture for molding toshape. The ceramic powders can be blended using a conventional V-coneblender, pneumatic blender, or other such blending equipment. The bindercan be added using conventional high-shear mixing equipment at roomtemperature or elevated temperature. The ceramic powders may comprisealumina, silica, zirconia, zircon, yttria, and other powders andmixtures thereof suitable for casting a particular metal or alloy. U.S.Pat. No. 4,837,187 describes an alumina based ceramic core made fromalumina and yttria flours. The particular ceramic powders, fugitivebinder and other constituents of the ceramic powder/binder mixture formno part of the invention as conventional ceramic powder and bindersystems can be used to form the ceramic core.

[0030] As described above in the Background Of The Invention section,the channels 14 d defined between wall features 14 c at the thincross-section trailing edge region 14 b of the molding cavity 14 havepresented manufacturing difficulties in that channels 14 d have beendifficult to completely fill with the fluid ceramic compound during thecore injection molding operation. In particular, the fluid ceramiccompound (binder material such as thermoplastic wax) solidifiesprematurely in the channels 14 d at their entrances to the main moldingcavity 14 and forces the ceramic compound to flow around the blockagesthrough the core print region 14 f to enter the channels 14 d (seearrows A) from the opposite outermost side of the trailing edge region14 b. During the so-called pack phase of the injection cycle, theprematurely solidified ceramic compound fronts located in the channels14 d are pushed and “forged” together trapping air between the fronts,resulting in formation of so-called weld or knit lines that arerelatively mechanically weak areas that can easily break or fractureduring normal core handling and processing, resulting in scrapping ofthe core. The problem of weak knit line formation has persisted forcertain core designs even though high die fill speeds (e.g. less than150 milliseconds), high ceramic compound temperatures (e.g. 290 degreesF.), and high pack pressures (e.g. 2000 psi) have been used in pastattempts to overcome the problem.

[0031] Pursuant to an embodiment of the invention, a local region 30 ofdie 10 or die 12, or both, proximate the trailing edge channels 14 d isheated prior to and during introduction of the fluid ceramic material orcompound followed by cooling of the local region(s) 30 before removal ofa ceramic core from the molding cavity 14. In an illustrative embodimentof the invention offered for purposes of illustrating and not limitingthe invention, the local region 30 of one or both of the dies isheated/cooled by one or more Peltier thermoelectric elements 40 disposedon In FIG. 2, thermoelectric element 40 is shown in detail while asimilar thermoelectric element 40′ is shown schematically by dashedlines. The invention can be practiced with one more thermoelectricelements 40 on die 10 or on die 12, or on both dies 10, 12, proximate tothe respective local region(s) 30 including the trailing edge channels14 d. If thermoelectric elements 40 are provided on both dies 10, 12,they typically will be of the same in type. Only the thermoelectricelements 40 on die 10 will be described below for sake of convenience,it being understood the thermoelectric element(s) on die 12 would besimilar.

[0032] Referring to FIGS. 2-3, die 10 is machined or otherwise formed toinclude one or more grooves 14 j (two grooves shown in FIG. 3)configured to receive a respective Peltier semiconductor thermoelectricelement 40 that can provide a heating effect or cooling effect dependingthe direction of electrical current flow through the element 40 from anelectrical power controller S, such as a voltage controller that canprovide a desired selected voltage magnitude and polarity. The grooves14 j are oriented at an angle to the parting surface PS of the die 10such that surface 14 s 1 of the grooves 14 j is generally parallel toand spaced about {fraction (5/32)} inch from the trailing edge region 14b of the molding cavity for purposes of illustration and not limitation.

[0033] Each Peltier thermoelectric (PTE) element 40 comprises acommercially available PTE element and includes a thermally conductivedielectric plate 40 a in thermal contact with the adjacent diegroove-forming surface 14 s 1, a thermally conductive dielectric plate40 b in thermal contact with a heat exchanger 42, and a plurality ofsemiconductors 40 c therebetween as is known. Suitable PTE elements 40for practicing the invention are commercially available from MelcorCorporation, Trenton, N.J. A thermally conductive boron nitride paste,aluminum nitride foil, or other thermally conductive material preferablyis placed between plate 40 a and die surface 14 s 1 and plate 40 b andheat exchanger 42. The boron nitride paste is available commerciallyfrom Advanced Ceramics Corporation, Cleveland, Ohio. The aluminumnitride foil is available commercially from Melcor Corporation, Trenton,N.J.

[0034] Each heat exchanger 42 comprises a hollow metal (e.g. copper) orother thermally conductive material manifold communicated to coolingfluid inlet conduit 42 a and cooling fluid outlet conduit 42 b. The heatexchanger 42 can include internal serpentine passages (not shown) forflow of the cooling fluid therethrough. The conduits 42 a, 42 b arereceived in a primary groove 10 b and secondary grooves 10 c of the die10 extending perpendicular to primary groove 10 b. The vent passages 14p communicate to grooves 10 b, 10 c to vent air from mold cavity 14during filling thereof with ceramic core material. The cooling fluid cancomprise compressed air, water, or other fluid such that the inletconduit 42 a is connected to a source of cooling water (e.g. shop water)or compressed air (e.g. compressed shop air) or other close or open loopfluid system. The outlet conduit 42 b for compressed air can becommunicated to ambient air. If a liquid (e.g. water) is used, theoutlet conduit 42 b is connected to a conventional sewer water drain orprovided in a closed loop recirculation system.

[0035] An alternative embodiment of the invention shown in FIG. 3A omitsthe heat exchanger 42 and places thermally conductive material 45′, suchas for example only boron nitride paste or aluminum nitride pad, betweenthe plate 40 b, and the adjacent die groove-forming surface 14 s 2 inFIG. 2 to provide thermal contact therebetween. The boron nitride pasteis available commercially from Advanced Ceramics Corporation, Cleveland,Ohio. The aluminum nitride pad or foil is available commercially fromMelcor Corporation, Trenton, N.J. In FIG. 3A, like features of FIGS. 1-3bear like reference numeral primed.

[0036] A thermocouple 50 is positioned in a bore in the die 10 tomonitor the temperature of the local die region 30. The thermocouple 50is connected to power controller S, such as the voltage controllerdescribed above, to provide feedback signals representative of senseddie temperature at the local die region 30 to the voltage controller.The thermocouple can be positioned at any position between surface 14 s1 and region 14 b in die 10 and/or 12 to this end. The voltagecontroller can be connected to the injection machine microprocessorcontroller MC so that thermal cycling (heating/cooling) of the local dieregion 30 pursuant to the invention can be coordinated with the fillstage and hold stage of press operation. The voltage controller S isconnected by lead wires W1, W2 to PTE elements 40 to provide a voltagemagnitude and polarity to the PTE elements 40 to heat or cool the localdie region 30 depending upon the stage of operation of the injectionmolding press.

[0037] For example, pursuant to an embodiment of the invention, localregion 30 of die 10 (and/or die 12) is heated prior to and during thefilling stage until the fluid ceramic core material fills the moldingcavity 14. Heating of the local region 30 by the PTE elements 40 iscontrolled by power controller S to provide an elevated superambienttemperature at the local die region 30 that will substantially preventpremature solidification of the liquid ceramic slurry before it fillsthe trailing edge channels 14 d. That is, the ceramic material remainsfluid until the channels 14 d are filled. The amount of heat energy thatmust be supplied to the local regions 30 by the PTE elements 40 willvary in dependence on the composition and temperature of the ceramiccore material being introduced, ambient air temperature, dietemperature, thermal conductivity of the die material, and core/diegeometric factors and can be determined empirically for given coremolding parameters.

[0038] For purposes of illustration and not limitation, the local dieregion 30 can be heated to a temperature of 160 degrees F. and above fora ceramic compound of the type described in U.S. Pat. No. 4,837,187having a solidification temperature in the range of 155 to 90 degrees F.and at a injection temperature of 290 degrees F. injected into steeldies at a flow rate of 11.5 cubic inches/second to achieve filling oftrailing edge channels 14 d of the type illustrated in FIGS. 1-2 withceramic compound such that the aforementioned mechanically weak weld orknit lines are completely eliminated at the trailing edge ceramic ribsR, FIG. 4.

[0039] At an empirically determined point after the fill stage, the PTEelements 40 are controlled to provide a cooling effect, rather than aheating effect, at the local die region 30 to cool that region to asuitable lower core ejection temperature that will permit removal of themolded core C from molding cavity 14 by movement of ejector pins EPwithout sticking of the trailing edge region 14 b to the surfaces of themolding cavity and without damage to the green core. To this end, thevoltage provided to the PTE elements 40 is reversed in direction andcontrolled by power controller S to provide a lower ejection temperatureat die region 30. A suitable ejection temperature to avoid sticking ofthe molded core (or molded pattern) to the molding cavity and coredamage, such as breaking, cracking, and/or distortion of the moldedcore, can be determined empirically for a given core (or pattern)molding operation. A typical second lower ejection temperature of thedie region 30 can be 85 degrees F. for the above ceramic core compoundand molding parameters described above to mold core C.

[0040] The above described cycling of the local die region between thefirst superambient temperature and second lower ejection temperatureenables molding of ceramic cores C of the type shown in FIG. 4 as wellas other cores with adequate green core strength and reduced scrappedcores due to the presence of weakened weld or knit lines at the ribs Rand without sticking problems when the core is removed from the moldingcavity 14. Moreover, reduced die fill speeds (e.g. greater than 150milliseconds), reduced core material temperatures, and reduced packpressures (e.g. less than 2000 psi) may be used. Reduced fill speeds areadvantageous to reduce wear of dies 10, 12 and reduce entrapped air inthe molded core or pattern.

[0041] After the green (unfired) core C is removed from the dies 10, 12it is sintered at elevated temperature in conventional manner to achieveconsolidation of the ceramic powder particles by heating to impartstrength to the core for use in the investment casting process.Sintering of the green ceramic core is achieved by means of heattreatment to an elevated temperature based on the requirements of theceramic powders employed. Above U.S. Pat. No. 4,837,187 describesthermal processing of an alumina based ceramic core. The particularthermal processing technique forms no part of the invention asconventional thermal processing techniques can be used to make thefired, porous ceramic core C, FIG. 4.

[0042] The invention has been described above with respect to use of PTEelements 40 to heat and then cool the local die region 30 since theseelements are durable, compact and relatively rapidly heat and cool thelocal die region 30 to accommodate short cycle times of the injectionmolding machine. The invention is not so limited as other heating andcooling devices or techniques may be used depending upon cycle times ofthe molding machine employed. For example, hot fluid heating and coldfluid cooling of the die region 30 using proximate oil or water passagesin the dies 10 and/or 12 or mold bases 27 a, 27 b may be used in theevent that longer machine cycle times are acceptable. Referring to FIG.3B where like features of previous figures are represented by likereference numerals double primed, lower die 10″, is shown including awater, oil or other fluid passage P1″ to heat and cool die region 30″proximate the trailing edge region 14 b″ of molding cavity 14″ and asimilar water, oil, or other fluid passage P2 ″ to heat and cool dieregion 31″ proximate a leading edge region 14 a″ of molding cavity 14″.The locations of the passages P1″, P2″ in the die 10″ and/or die 12″proximate to regions 30″ and 31″ can be selected empirically to provideheating and cooling thereof as described above to achieve the benefitsof the invention. A manifold M″ can supply the water, oil or other fluidto passages P1″, P2″. The manifold M″ is communicated by lines orconduits L1″, L2″ alternately to a fluid heater H″ (e.g. a 18 kilowattelectrical hot water heater) to provide hot fluid at a suitabletemperature (e.g. hot water at 140 to 160 degrees F.) to passages P1″,P2″ to heat die regions 30″, 31″. The manifold M″ then is communicatedto a fluid chiller CH″ (e.g. conventional water chiller) to providecooled fluid at a suitable temperature (e.g. cold water at 45 degreesF.) to passages P1″, P2″ to cool die regions 30″, 31″ to the ejectiontemperature as described above. After the regions 30″, 31″ are cooleddown to the core ejection temperature, fluid flow through passages P1″,P2″ can be terminated. The manifold M″ and passages P1″, P2″ areconnected in closed loop manner by return lines LR″ with the fluidheater H″ and fluid chiller CH″ with conventional valves V″ provided andcontrolled in a manner to alternately communicate the manifold M″ to theheater H″ or chiller CH″ as needed to heat and then cool die regions30″, 31″. The fluid supply lines or conduits L″, L2″ can includeconventional check valves (not shown) to prevent reverse flow. Theheater H″ and chiller CH″ are controlled in response to temperaturesensed by thermocouple 50″. Although not shown, the upper die (notshown) can include similar fluid passages as passages P1″, P2″ to thissame. Either one or both of dies 10″, 12″ can includes such fluidpassages.

[0043] Those skilled in the art will appreciate that the invention canbe practiced using a combination of the thermoelectric elements 40 andone or more fluid passages described above to heat and cool one or morehard-to-fill regions of the molding cavity 14 in practice of theinvention.

[0044] Moreover, although the invention has been described above withrespect to heating and cooling of one or more hard-to-fill regions ofthe molding cavity 14, it is not limited in this manner in that the dies10 and/or 12 can be generally, rather than locally, heat and cooled toimprove filling of the molding cavity. For example, oil, water or otherfluid passages can be provided throughout one or both dies 10, 12 in aconfiguration necessary to provide general heating and cooling of thedie(s) to heat and cool one or more hard-to-fill regions of moldingcavity 14 pursuant to another embodiment of the invention to improvefilling thereof.

[0045] In addition, the invention can be practiced in manufacture of asolid fugitive pattern, or a fugitive pattern injected about the ceramiccore C. For example, the ceramic core C of FIG. 4 typically is placedbetween pattern molding dies (not shown) forming a pattern moldingcavity, and then molten pattern material, such as wax, is injected underpressure about the core in the pattern molding cavity. Such a procedureis described in U.S. Pat. No. 5,296,308 and a filled pattern waxmaterial employed to form a pattern is described in U.S. Pat. No.5,983,982, the teachings of both of which patents are incorporatedherein by reference. Pattern materials can be selected from pattern waxmaterials, pattern polymer materials (e.g. polyurethane, polystyrene,and others) and others known in the lost wax investment casting art toproduce a fugitive pattern that is invested in a ceramic shell mold andthen subsequently removed thermally or by other means from the shellmold. The trailing edge of the fugitive pattern is molded to fill thespaces between the ceramic ribs R of the core C, FIG. 4, and form a thincross-section trailing edge region on the pattern.

[0046] The invention envisions heating and cooling at least the trailingedge region of the pattern molding cavity in a manner similar to thatdescribed above for the core molding cavity 14 to insure completefilling of the spaces between the ceramic ribs R and other details ofthe trailing edge region without damaging the core while the patternmaterial (e.g. wax) remains molten and then cooling to a second lowerpattern ejection temperature to permit removal of the fugitive patternwithout sticking to the die surfaces. The invention envisions similarlyheating/cooling other regions of the pattern molding cavity, such as theleading edge region, as necessary to fill one or more hard-to-fillregions thereof. The invention also envisions generally, rather thanlocally, heating and cooling of one or both pattern molding dies to thissame end.

[0047] Although the invention has been described with respect to certainembodiments thereof, those skilled in the art will appreciate that theinvention is not limited to these embodiments and changes,modifications, and the like can be made therein within the scope of theinvention as set forth in the appended claims.

We claim:
 1. A method of making a molded body for use in investmentcasting, comprising filling a molding cavity disposed betweencooperating dies with a fluid material selected to form a ceramic coreor a fugitive pattern, heating at least a region of at least one of saiddies to a superambient temperature during filling of said moldingcavity, and cooling said local region to a lower temperature beforeremoval of a molded body from said molding cavity.
 2. The method ofclaim 1 wherein said region of said at least one of said dies is heatedand cooled by at least one thermoelectric element disposed thereon. 3.The method of claim 2 including sensing temperature of said region andcontrolling said at least one thermoelectric element in response tosensed temperature.
 4. The method of claim 2 wherein said regioncomprises a trailing edge-shaped region of an airfoil, said trailingedge-shaped region being heated prior to and during filling of saidmolding cavity and cooled before removal of said molded body from saidmolding cavity.
 5. The method of claim 4 wherein said trailingedge-shaped region includes relatively narrow channels that are heatedby said at least one thermoelectric element to permit filling thereofwith said fluid material.
 6. The method of claim 1 wherein said regionof said at least one of said dies is heated and cooled by at least onefluid passage disposed therein.
 7. The method of claim 2 includingremoving heat from said at least one thermoelectric element using a heatexchange fluid.
 8. The method of claim 7 wherein said heat exchangefluid is selected from the group consisting of a liquid and gas.
 9. Themethod of claim 1 wherein said fluid material comprises a ceramic corematerial comprising ceramic flour and a fluid binder.
 10. The method ofclaim 1 wherein said fluid material comprises a pattern materialselected from the group consisting of a wax and a polymer.
 11. Apparatusfor molding an airfoil-shaped body for use in casting a metallicairfoil, comprising first and second dies defining a molding cavityhaving an airfoil-shaped cavity, and at least one thermoelectric elementdisposed on at least one of said dies to heat at least a hard-to-fillregion of said cavity to a superambient temperature during filling ofsaid molding cavity with a fluid material, and to cool said region to alower temperature before an airfoil-shaped body is removed from saidmolding cavity.
 12. The apparatus of claim 11 including a temperaturesensor proximate said region and an electrical power controllerconnected to said at least one thermoelectric element to controlelectrical power thereto in response to sensed temperature.
 13. Theapparatus of claim 11 including a heat exchanger in thermal contact withsaid thermoelectric element.
 14. The apparatus of claim 13 including aninlet conduit conducting a heat exchange fluid to said heat exchanger toremove heat therefrom and an outlet conduit for exhausting said heatexchange fluid.
 15. The apparatus of claim 11 including a thermallyconductive material disposed between said at least one thermoelectricelement and said at least one of said dies for conducting heat from saidat least one thermoelectric element.
 16. The apparatus of claim 11wherein said molding cavity has a configuration of a ceramic core. 17.The apparatus of claim 11 wherein said molding cavity has aconfiguration corresponding to a pattern that replicates saidairfoil-shaped body.
 18. Apparatus for molding an airfoil-shaped bodyfor use in casting a metallic airfoil, comprising first and second diesdefining a molding cavity having an airfoil-shaped cavity, and at leastone fluid passage on at least one of said dies to provide a fluid toheat at least a hard-to-fill region of said cavity to a superambienttemperature during filling of said molding cavity with a fluid material,and to cool said region to a lower temperature before an airfoil-shapedbody is removed from said molding cavity.
 19. The apparatus of claim 18wherein said molding cavity has a configuration of a ceramic core. 20.The apparatus of claim 18 wherein said molding cavity has aconfiguration corresponding to a pattern that replicates saidairfoil-shaped body.